Does consistently performing supererogatory prayers after the obligatory prayers (two rak'ahs after Fajr, Dhuhr, and Isha, and three rak'ahs after Maghrib) equate to praying for 70 years?

What is mentioned in the question is legally baseless. For a supererogatory act to be equivalent to such and such an act of worship can only be established by a divine text, and no such text exists. Furthermore, performing three supererogatory rak'ahs after Maghrib and two after Fajr is legally forbidden. Persisting in a specific number of voluntary prayers for which there is no command from the Lawgiver to persist in them may lead to an innovative Bid'ah. It is advisable to refer to books of Sunnah and Fiqh to learn about the prescribed supererogatory acts.